/*
 * Copyright (c) 1999, 2015, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package com.sun.tools.javac.jvm;

import com.sun.tools.javac.code.*;
import com.sun.tools.javac.code.Symbol.*;
import com.sun.tools.javac.code.Types.UniqueType;
import com.sun.tools.javac.tree.JCTree;
import com.sun.tools.javac.util.*;
import com.sun.tools.javac.util.JCDiagnostic.DiagnosticPosition;

import static com.sun.tools.javac.code.TypeTag.BOT;
import static com.sun.tools.javac.code.TypeTag.INT;
import static com.sun.tools.javac.jvm.ByteCodes.*;
import static com.sun.tools.javac.jvm.UninitializedType.*;
import static com.sun.tools.javac.jvm.ClassWriter.StackMapTableFrame;

An internal structure that corresponds to the code attribute of
 methods in a classfile. The class also provides some utility operations to
 generate bytecode instructions.
 
This is NOT part of any supported API.
 If you write code that depends on this, you do so at your own risk.
 This code and its internal interfaces are subject to change or
 deletion without notice.
/** An internal structure that corresponds to the code attribute of
 *  methods in a classfile. The class also provides some utility operations to
 *  generate bytecode instructions.
 *
 *  <p><b>This is NOT part of any supported API.
 *  If you write code that depends on this, you do so at your own risk.
 *  This code and its internal interfaces are subject to change or
 *  deletion without notice.</b>
 */
public class Code {

    public final boolean debugCode;
    public final boolean needStackMap;

    public enum StackMapFormat {
        NONE,
        CLDC {
            Name getAttributeName(Names names) {
                return names.StackMap;
            }
        },
        JSR202 {
            Name getAttributeName(Names names) {
                return names.StackMapTable;
            }
        };
        Name getAttributeName(Names names) {
            return names.empty;
        }
    }

    final Types types;
    final Symtab syms;

/*---------- classfile fields: --------------- */

    
The maximum stack size.
/** The maximum stack size.
     */
    public int max_stack = 0;

    
The maximum number of local variable slots.
/** The maximum number of local variable slots.
     */
    public int max_locals = 0;

    
The code buffer.
/** The code buffer.
     */
    public byte[] code = new byte[64];

    
the current code pointer.
/** the current code pointer.
     */
    public int cp = 0;

    
Check the code against VM spec limits; if
 problems report them and return true.
/** Check the code against VM spec limits; if
     *  problems report them and return true.
     */
    public boolean checkLimits(DiagnosticPosition pos, Log log) {
        if (cp > ClassFile.MAX_CODE) {
            log.error(pos, "limit.code");
            return true;
        }
        if (max_locals > ClassFile.MAX_LOCALS) {
            log.error(pos, "limit.locals");
            return true;
        }
        if (max_stack > ClassFile.MAX_STACK) {
            log.error(pos, "limit.stack");
            return true;
        }
        return false;
    }

    
A buffer for expression catch data. Each enter is a vector
 of four unsigned shorts.
/** A buffer for expression catch data. Each enter is a vector
     *  of four unsigned shorts.
     */
    ListBuffer<char[]> catchInfo = new ListBuffer<>();

    
A buffer for line number information. Each entry is a vector
 of two unsigned shorts.
/** A buffer for line number information. Each entry is a vector
     *  of two unsigned shorts.
     */
    List<char[]> lineInfo = List.nil(); // handled in stack fashion

    
The CharacterRangeTable
/** The CharacterRangeTable
     */
    public CRTable crt;

/*---------- internal fields: --------------- */

    
Are we generating code with jumps ≥ 32K?
/** Are we generating code with jumps &ge; 32K?
     */
    public boolean fatcode;

    
Code generation enabled?
/** Code generation enabled?
     */
    private boolean alive = true;

    
The current machine state (registers and stack).
/** The current machine state (registers and stack).
     */
    State state;

    
Is it forbidden to compactify code, because something is
 pointing to current location?
/** Is it forbidden to compactify code, because something is
     *  pointing to current location?
     */
    private boolean fixedPc = false;

    
The next available register.
/** The next available register.
     */
    public int nextreg = 0;

    
A chain for jumps to be resolved before the next opcode is emitted.
 We do this lazily to avoid jumps to jumps.
/** A chain for jumps to be resolved before the next opcode is emitted.
     *  We do this lazily to avoid jumps to jumps.
     */
    Chain pendingJumps = null;

    
The position of the currently statement, if we are at the
 start of this statement, NOPOS otherwise.
 We need this to emit line numbers lazily, which we need to do
 because of jump-to-jump optimization.
/** The position of the currently statement, if we are at the
     *  start of this statement, NOPOS otherwise.
     *  We need this to emit line numbers lazily, which we need to do
     *  because of jump-to-jump optimization.
     */
    int pendingStatPos = Position.NOPOS;

    
Set true when a stackMap is needed at the current PC. /** Set true when a stackMap is needed at the current PC. */
    boolean pendingStackMap = false;

    
The stack map format to be generated. /** The stack map format to be generated. */
    StackMapFormat stackMap;

    
Switch: emit variable debug info.
/** Switch: emit variable debug info.
     */
    boolean varDebugInfo;

    
Switch: emit line number info.
/** Switch: emit line number info.
     */
    boolean lineDebugInfo;

    
Emit line number info if map supplied
/** Emit line number info if map supplied
     */
    Position.LineMap lineMap;

    
The constant pool of the current class.
/** The constant pool of the current class.
     */
    final Pool pool;

    final MethodSymbol meth;

    
Construct a code object, given the settings of the fatcode,
 debugging info switches and the CharacterRangeTable.
/** Construct a code object, given the settings of the fatcode,
     *  debugging info switches and the CharacterRangeTable.
     */
    public Code(MethodSymbol meth,
                boolean fatcode,
                Position.LineMap lineMap,
                boolean varDebugInfo,
                StackMapFormat stackMap,
                boolean debugCode,
                CRTable crt,
                Symtab syms,
                Types types,
                Pool pool) {
        this.meth = meth;
        this.fatcode = fatcode;
        this.lineMap = lineMap;
        this.lineDebugInfo = lineMap != null;
        this.varDebugInfo = varDebugInfo;
        this.crt = crt;
        this.syms = syms;
        this.types = types;
        this.debugCode = debugCode;
        this.stackMap = stackMap;
        switch (stackMap) {
        case CLDC:
        case JSR202:
            this.needStackMap = true;
            break;
        default:
            this.needStackMap = false;
        }
        state = new State();
        lvar = new LocalVar[20];
        this.pool = pool;
    }


/* **************************************************************************
 * Typecodes & related stuff
 ****************************************************************************/

    
Given a type, return its type code (used implicitly in the
 JVM architecture).
/** Given a type, return its type code (used implicitly in the
     *  JVM architecture).
     */
    public static int typecode(Type type) {
        switch (type.getTag()) {
        case BYTE: return BYTEcode;
        case SHORT: return SHORTcode;
        case CHAR: return CHARcode;
        case INT: return INTcode;
        case LONG: return LONGcode;
        case FLOAT: return FLOATcode;
        case DOUBLE: return DOUBLEcode;
        case BOOLEAN: return BYTEcode;
        case VOID: return VOIDcode;
        case CLASS:
        case ARRAY:
        case METHOD:
        case BOT:
        case TYPEVAR:
        case UNINITIALIZED_THIS:
        case UNINITIALIZED_OBJECT:
            return OBJECTcode;
        default: throw new AssertionError("typecode " + type.getTag());
        }
    }

    
Collapse type code for subtypes of int to INTcode.
/** Collapse type code for subtypes of int to INTcode.
     */
    public static int truncate(int tc) {
        switch (tc) {
        case BYTEcode: case SHORTcode: case CHARcode: return INTcode;
        default: return tc;
        }
    }

    
The width in bytes of objects of the type.
/** The width in bytes of objects of the type.
     */
    public static int width(int typecode) {
        switch (typecode) {
        case LONGcode: case DOUBLEcode: return 2;
        case VOIDcode: return 0;
        default: return 1;
        }
    }

    public static int width(Type type) {
        return type == null ? 1 : width(typecode(type));
    }

    
The total width taken up by a vector of objects.
/** The total width taken up by a vector of objects.
     */
    public static int width(List<Type> types) {
        int w = 0;
        for (List<Type> l = types; l.nonEmpty(); l = l.tail)
            w = w + width(l.head);
        return w;
    }

    
Given a type, return its code for allocating arrays of that type.
/** Given a type, return its code for allocating arrays of that type.
     */
    public static int arraycode(Type type) {
        switch (type.getTag()) {
        case BYTE: return 8;
        case BOOLEAN: return 4;
        case SHORT: return 9;
        case CHAR: return 5;
        case INT: return 10;
        case LONG: return 11;
        case FLOAT: return 6;
        case DOUBLE: return 7;
        case CLASS: return 0;
        case ARRAY: return 1;
        default: throw new AssertionError("arraycode " + type);
        }
    }


/* **************************************************************************
 * Emit code
 ****************************************************************************/

    
The current output code pointer.
/** The current output code pointer.
     */
    public int curCP() {
        /*
         * This method has side-effects because calling it can indirectly provoke
         *  extra code generation, like goto instructions, depending on the context
         *  where it's called.
         *  Use with care or even better avoid using it.
         */
        if (pendingJumps != null) {
            resolvePending();
        }
        if (pendingStatPos != Position.NOPOS) {
            markStatBegin();
        }
        fixedPc = true;
        return cp;
    }

    
Emit a byte of code.
/** Emit a byte of code.
     */
    private  void emit1(int od) {
        if (!alive) return;
        code = ArrayUtils.ensureCapacity(code, cp);
        code[cp++] = (byte)od;
    }

    
Emit two bytes of code.
/** Emit two bytes of code.
     */
    private void emit2(int od) {
        if (!alive) return;
        if (cp + 2 > code.length) {
            emit1(od >> 8);
            emit1(od);
        } else {
            code[cp++] = (byte)(od >> 8);
            code[cp++] = (byte)od;
        }
    }

    
Emit four bytes of code.
/** Emit four bytes of code.
     */
    public void emit4(int od) {
        if (!alive) return;
        if (cp + 4 > code.length) {
            emit1(od >> 24);
            emit1(od >> 16);
            emit1(od >> 8);
            emit1(od);
        } else {
            code[cp++] = (byte)(od >> 24);
            code[cp++] = (byte)(od >> 16);
            code[cp++] = (byte)(od >> 8);
            code[cp++] = (byte)od;
        }
    }

    
Emit an opcode.
/** Emit an opcode.
     */
    private void emitop(int op) {
        if (pendingJumps != null) resolvePending();
        if (alive) {
            if (pendingStatPos != Position.NOPOS)
                markStatBegin();
            if (pendingStackMap) {
                pendingStackMap = false;
                emitStackMap();
            }
            if (debugCode)
                System.err.println("emit@" + cp + " stack=" +
                                   state.stacksize + ": " +
                                   mnem(op));
            emit1(op);
        }
    }

    void postop() {
        Assert.check(alive || state.stacksize == 0);
    }

    
Emit a ldc (or ldc_w) instruction, taking into account operand size
/** Emit a ldc (or ldc_w) instruction, taking into account operand size
    */
    public void emitLdc(int od) {
        if (od <= 255) {
            emitop1(ldc1, od);
        }
        else {
            emitop2(ldc2, od);
        }
    }

    
Emit a multinewarray instruction.
/** Emit a multinewarray instruction.
     */
    public void emitMultianewarray(int ndims, int type, Type arrayType) {
        emitop(multianewarray);
        if (!alive) return;
        emit2(type);
        emit1(ndims);
        state.pop(ndims);
        state.push(arrayType);
    }

    
Emit newarray.
/** Emit newarray.
     */
    public void emitNewarray(int elemcode, Type arrayType) {
        emitop(newarray);
        if (!alive) return;
        emit1(elemcode);
        state.pop(1); // count
        state.push(arrayType);
    }

    
Emit anewarray.
/** Emit anewarray.
     */
    public void emitAnewarray(int od, Type arrayType) {
        emitop(anewarray);
        if (!alive) return;
        emit2(od);
        state.pop(1);
        state.push(arrayType);
    }

    
Emit an invokeinterface instruction.
/** Emit an invokeinterface instruction.
     */
    public void emitInvokeinterface(int meth, Type mtype) {
        int argsize = width(mtype.getParameterTypes());
        emitop(invokeinterface);
        if (!alive) return;
        emit2(meth);
        emit1(argsize + 1);
        emit1(0);
        state.pop(argsize + 1);
        state.push(mtype.getReturnType());
    }

    
Emit an invokespecial instruction.
/** Emit an invokespecial instruction.
     */
    public void emitInvokespecial(int meth, Type mtype) {
        int argsize = width(mtype.getParameterTypes());
        emitop(invokespecial);
        if (!alive) return;
        emit2(meth);
        Symbol sym = (Symbol)pool.pool[meth];
        state.pop(argsize);
        if (sym.isConstructor())
            state.markInitialized((UninitializedType)state.peek());
        state.pop(1);
        state.push(mtype.getReturnType());
    }

    
Emit an invokestatic instruction.
/** Emit an invokestatic instruction.
     */
    public void emitInvokestatic(int meth, Type mtype) {
        int argsize = width(mtype.getParameterTypes());
        emitop(invokestatic);
        if (!alive) return;
        emit2(meth);
        state.pop(argsize);
        state.push(mtype.getReturnType());
    }

    
Emit an invokevirtual instruction.
/** Emit an invokevirtual instruction.
     */
    public void emitInvokevirtual(int meth, Type mtype) {
        int argsize = width(mtype.getParameterTypes());
        emitop(invokevirtual);
        if (!alive) return;
        emit2(meth);
        state.pop(argsize + 1);
        state.push(mtype.getReturnType());
    }

    
Emit an invokedynamic instruction.
/** Emit an invokedynamic instruction.
     */
    public void emitInvokedynamic(int desc, Type mtype) {
        int argsize = width(mtype.getParameterTypes());
        emitop(invokedynamic);
        if (!alive) return;
        emit2(desc);
        emit2(0);
        state.pop(argsize);
        state.push(mtype.getReturnType());
    }

    
Emit an opcode with no operand field.
/** Emit an opcode with no operand field.
     */
    public void emitop0(int op) {
        emitop(op);
        if (!alive) return;
        switch (op) {
        case aaload: {
            state.pop(1);// index
            Type a = state.stack[state.stacksize-1];
            Assert.check(!a.hasTag(BOT)); // null type as is cannot be indexed.
            state.pop(1);
            state.push(types.erasure(types.elemtype(a))); }
            break;
        case goto_:
            markDead();
            break;
        case nop:
        case ineg:
        case lneg:
        case fneg:
        case dneg:
            break;
        case aconst_null:
            state.push(syms.botType);
            break;
        case iconst_m1:
        case iconst_0:
        case iconst_1:
        case iconst_2:
        case iconst_3:
        case iconst_4:
        case iconst_5:
        case iload_0:
        case iload_1:
        case iload_2:
        case iload_3:
            state.push(syms.intType);
            break;
        case lconst_0:
        case lconst_1:
        case lload_0:
        case lload_1:
        case lload_2:
        case lload_3:
            state.push(syms.longType);
            break;
        case fconst_0:
        case fconst_1:
        case fconst_2:
        case fload_0:
        case fload_1:
        case fload_2:
        case fload_3:
            state.push(syms.floatType);
            break;
        case dconst_0:
        case dconst_1:
        case dload_0:
        case dload_1:
        case dload_2:
        case dload_3:
            state.push(syms.doubleType);
            break;
        case aload_0:
            state.push(lvar[0].sym.type);
            break;
        case aload_1:
            state.push(lvar[1].sym.type);
            break;
        case aload_2:
            state.push(lvar[2].sym.type);
            break;
        case aload_3:
            state.push(lvar[3].sym.type);
            break;
        case iaload:
        case baload:
        case caload:
        case saload:
            state.pop(2);
            state.push(syms.intType);
            break;
        case laload:
            state.pop(2);
            state.push(syms.longType);
            break;
        case faload:
            state.pop(2);
            state.push(syms.floatType);
            break;
        case daload:
            state.pop(2);
            state.push(syms.doubleType);
            break;
        case istore_0:
        case istore_1:
        case istore_2:
        case istore_3:
        case fstore_0:
        case fstore_1:
        case fstore_2:
        case fstore_3:
        case astore_0:
        case astore_1:
        case astore_2:
        case astore_3:
        case pop:
        case lshr:
        case lshl:
        case lushr:
            state.pop(1);
            break;
        case areturn:
        case ireturn:
        case freturn:
            Assert.check(state.nlocks == 0);
            state.pop(1);
            markDead();
            break;
        case athrow:
            state.pop(1);
            markDead();
            break;
        case lstore_0:
        case lstore_1:
        case lstore_2:
        case lstore_3:
        case dstore_0:
        case dstore_1:
        case dstore_2:
        case dstore_3:
        case pop2:
            state.pop(2);
            break;
        case lreturn:
        case dreturn:
            Assert.check(state.nlocks == 0);
            state.pop(2);
            markDead();
            break;
        case dup:
            state.push(state.stack[state.stacksize-1]);
            break;
        case return_:
            Assert.check(state.nlocks == 0);
            markDead();
            break;
        case arraylength:
            state.pop(1);
            state.push(syms.intType);
            break;
        case isub:
        case iadd:
        case imul:
        case idiv:
        case imod:
        case ishl:
        case ishr:
        case iushr:
        case iand:
        case ior:
        case ixor:
            state.pop(1);
            // state.pop(1);
            // state.push(syms.intType);
            break;
        case aastore:
            state.pop(3);
            break;
        case land:
        case lor:
        case lxor:
        case lmod:
        case ldiv:
        case lmul:
        case lsub:
        case ladd:
            state.pop(2);
            break;
        case lcmp:
            state.pop(4);
            state.push(syms.intType);
            break;
        case l2i:
            state.pop(2);
            state.push(syms.intType);
            break;
        case i2l:
            state.pop(1);
            state.push(syms.longType);
            break;
        case i2f:
            state.pop(1);
            state.push(syms.floatType);
            break;
        case i2d:
            state.pop(1);
            state.push(syms.doubleType);
            break;
        case l2f:
            state.pop(2);
            state.push(syms.floatType);
            break;
        case l2d:
            state.pop(2);
            state.push(syms.doubleType);
            break;
        case f2i:
            state.pop(1);
            state.push(syms.intType);
            break;
        case f2l:
            state.pop(1);
            state.push(syms.longType);
            break;
        case f2d:
            state.pop(1);
            state.push(syms.doubleType);
            break;
        case d2i:
            state.pop(2);
            state.push(syms.intType);
            break;
        case d2l:
            state.pop(2);
            state.push(syms.longType);
            break;
        case d2f:
            state.pop(2);
            state.push(syms.floatType);
            break;
        case tableswitch:
        case lookupswitch:
            state.pop(1);
            // the caller is responsible for patching up the state
            break;
        case dup_x1: {
            Type val1 = state.pop1();
            Type val2 = state.pop1();
            state.push(val1);
            state.push(val2);
            state.push(val1);
            break;
        }
        case bastore:
            state.pop(3);
            break;
        case int2byte:
        case int2char:
        case int2short:
            break;
        case fmul:
        case fadd:
        case fsub:
        case fdiv:
        case fmod:
            state.pop(1);
            break;
        case castore:
        case iastore:
        case fastore:
        case sastore:
            state.pop(3);
            break;
        case lastore:
        case dastore:
            state.pop(4);
            break;
        case dup2:
            if (state.stack[state.stacksize-1] != null) {
                Type value1 = state.pop1();
                Type value2 = state.pop1();
                state.push(value2);
                state.push(value1);
                state.push(value2);
                state.push(value1);
            } else {
                Type value = state.pop2();
                state.push(value);
                state.push(value);
            }
            break;
        case dup2_x1:
            if (state.stack[state.stacksize-1] != null) {
                Type value1 = state.pop1();
                Type value2 = state.pop1();
                Type value3 = state.pop1();
                state.push(value2);
                state.push(value1);
                state.push(value3);
                state.push(value2);
                state.push(value1);
            } else {
                Type value1 = state.pop2();
                Type value2 = state.pop1();
                state.push(value1);
                state.push(value2);
                state.push(value1);
            }
            break;
        case dup2_x2:
            if (state.stack[state.stacksize-1] != null) {
                Type value1 = state.pop1();
                Type value2 = state.pop1();
                if (state.stack[state.stacksize-1] != null) {
                    // form 1
                    Type value3 = state.pop1();
                    Type value4 = state.pop1();
                    state.push(value2);
                    state.push(value1);
                    state.push(value4);
                    state.push(value3);
                    state.push(value2);
                    state.push(value1);
                } else {
                    // form 3
                    Type value3 = state.pop2();
                    state.push(value2);
                    state.push(value1);
                    state.push(value3);
                    state.push(value2);
                    state.push(value1);
                }
            } else {
                Type value1 = state.pop2();
                if (state.stack[state.stacksize-1] != null) {
                    // form 2
                    Type value2 = state.pop1();
                    Type value3 = state.pop1();
                    state.push(value1);
                    state.push(value3);
                    state.push(value2);
                    state.push(value1);
                } else {
                    // form 4
                    Type value2 = state.pop2();
                    state.push(value1);
                    state.push(value2);
                    state.push(value1);
                }
            }
            break;
        case dup_x2: {
            Type value1 = state.pop1();
            if (state.stack[state.stacksize-1] != null) {
                // form 1
                Type value2 = state.pop1();
                Type value3 = state.pop1();
                state.push(value1);
                state.push(value3);
                state.push(value2);
                state.push(value1);
            } else {
                // form 2
                Type value2 = state.pop2();
                state.push(value1);
                state.push(value2);
                state.push(value1);
            }
        }
            break;
        case fcmpl:
        case fcmpg:
            state.pop(2);
            state.push(syms.intType);
            break;
        case dcmpl:
        case dcmpg:
            state.pop(4);
            state.push(syms.intType);
            break;
        case swap: {
            Type value1 = state.pop1();
            Type value2 = state.pop1();
            state.push(value1);
            state.push(value2);
            break;
        }
        case dadd:
        case dsub:
        case dmul:
        case ddiv:
        case dmod:
            state.pop(2);
            break;
        case ret:
            markDead();
            break;
        case wide:
            // must be handled by the caller.
            return;
        case monitorenter:
        case monitorexit:
            state.pop(1);
            break;

        default:
            throw new AssertionError(mnem(op));
        }
        postop();
    }

    
Emit an opcode with a one-byte operand field.
/** Emit an opcode with a one-byte operand field.
     */
    public void emitop1(int op, int od) {
        emitop(op);
        if (!alive) return;
        emit1(od);
        switch (op) {
        case bipush:
            state.push(syms.intType);
            break;
        case ldc1:
            state.push(typeForPool(pool.pool[od]));
            break;
        default:
            throw new AssertionError(mnem(op));
        }
        postop();
    }

    
The type of a constant pool entry. /** The type of a constant pool entry. */
    private Type typeForPool(Object o) {
        if (o instanceof Integer) return syms.intType;
        if (o instanceof Float) return syms.floatType;
        if (o instanceof String) return syms.stringType;
        if (o instanceof Long) return syms.longType;
        if (o instanceof Double) return syms.doubleType;
        if (o instanceof ClassSymbol) return syms.classType;
        if (o instanceof Pool.MethodHandle) return syms.methodHandleType;
        if (o instanceof UniqueType) return typeForPool(((UniqueType)o).type);
        if (o instanceof Type) {
            Type ty = (Type) o;

            if (ty instanceof Type.ArrayType) return syms.classType;
            if (ty instanceof Type.MethodType) return syms.methodTypeType;
        }
        throw new AssertionError("Invalid type of constant pool entry: " + o.getClass());
    }

    
Emit an opcode with a one-byte operand field;
 widen if field does not fit in a byte.
/** Emit an opcode with a one-byte operand field;
     *  widen if field does not fit in a byte.
     */
    public void emitop1w(int op, int od) {
        if (od > 0xFF) {
            emitop(wide);
            emitop(op);
            emit2(od);
        } else {
            emitop(op);
            emit1(od);
        }
        if (!alive) return;
        switch (op) {
        case iload:
            state.push(syms.intType);
            break;
        case lload:
            state.push(syms.longType);
            break;
        case fload:
            state.push(syms.floatType);
            break;
        case dload:
            state.push(syms.doubleType);
            break;
        case aload:
            state.push(lvar[od].sym.type);
            break;
        case lstore:
        case dstore:
            state.pop(2);
            break;
        case istore:
        case fstore:
        case astore:
            state.pop(1);
            break;
        case ret:
            markDead();
            break;
        default:
            throw new AssertionError(mnem(op));
        }
        postop();
    }

    
Emit an opcode with two one-byte operand fields;
 widen if either field does not fit in a byte.
/** Emit an opcode with two one-byte operand fields;
     *  widen if either field does not fit in a byte.
     */
    public void emitop1w(int op, int od1, int od2) {
        if (od1 > 0xFF || od2 < -128 || od2 > 127) {
            emitop(wide);
            emitop(op);
            emit2(od1);
            emit2(od2);
        } else {
            emitop(op);
            emit1(od1);
            emit1(od2);
        }
        if (!alive) return;
        switch (op) {
        case iinc:
            break;
        default:
            throw new AssertionError(mnem(op));
        }
    }

    
Emit an opcode with a two-byte operand field.
/** Emit an opcode with a two-byte operand field.
     */
    public void emitop2(int op, int od) {
        emitop(op);
        if (!alive) return;
        emit2(od);
        switch (op) {
        case getstatic:
            state.push(((Symbol)(pool.pool[od])).erasure(types));
            break;
        case putstatic:
            state.pop(((Symbol)(pool.pool[od])).erasure(types));
            break;
        case new_:
            Symbol sym;
            if (pool.pool[od] instanceof UniqueType) {
                // Required by change in Gen.makeRef to allow
                // annotated types.
                // TODO: is this needed anywhere else?
                sym = ((UniqueType)(pool.pool[od])).type.tsym;
            } else {
                sym = (Symbol)(pool.pool[od]);
            }
            state.push(uninitializedObject(sym.erasure(types), cp-3));
            break;
        case sipush:
            state.push(syms.intType);
            break;
        case if_acmp_null:
        case if_acmp_nonnull:
        case ifeq:
        case ifne:
        case iflt:
        case ifge:
        case ifgt:
        case ifle:
            state.pop(1);
            break;
        case if_icmpeq:
        case if_icmpne:
        case if_icmplt:
        case if_icmpge:
        case if_icmpgt:
        case if_icmple:
        case if_acmpeq:
        case if_acmpne:
            state.pop(2);
            break;
        case goto_:
            markDead();
            break;
        case putfield:
            state.pop(((Symbol)(pool.pool[od])).erasure(types));
            state.pop(1); // object ref
            break;
        case getfield:
            state.pop(1); // object ref
            state.push(((Symbol)(pool.pool[od])).erasure(types));
            break;
        case checkcast: {
            state.pop(1); // object ref
            Object o = pool.pool[od];
            Type t = (o instanceof Symbol)
                ? ((Symbol)o).erasure(types)
                : types.erasure((((UniqueType)o).type));
            state.push(t);
            break; }
        case ldc2w:
            state.push(typeForPool(pool.pool[od]));
            break;
        case instanceof_:
            state.pop(1);
            state.push(syms.intType);
            break;
        case ldc2:
            state.push(typeForPool(pool.pool[od]));
            break;
        case jsr:
            break;
        default:
            throw new AssertionError(mnem(op));
        }
        // postop();
    }

    
Emit an opcode with a four-byte operand field.
/** Emit an opcode with a four-byte operand field.
     */
    public void emitop4(int op, int od) {
        emitop(op);
        if (!alive) return;
        emit4(od);
        switch (op) {
        case goto_w:
            markDead();
            break;
        case jsr_w:
            break;
        default:
            throw new AssertionError(mnem(op));
        }
        // postop();
    }

    
Align code pointer to next `incr' boundary.
/** Align code pointer to next `incr' boundary.
     */
    public void align(int incr) {
        if (alive)
            while (cp % incr != 0) emitop0(nop);
    }

    
Place a byte into code at address pc. Pre: pc + 1 <= cp . /** Place a byte into code at address pc.
     *  Pre: {@literal pc + 1 <= cp }.
     */
    private void put1(int pc, int op) {
        code[pc] = (byte)op;
    }

    
Place two bytes into code at address pc. Pre: pc + 2 <= cp . /** Place two bytes into code at address pc.
     *  Pre: {@literal pc + 2 <= cp }.
     */
    private void put2(int pc, int od) {
        // pre: pc + 2 <= cp
        put1(pc, od >> 8);
        put1(pc+1, od);
    }

    
Place four bytes into code at address pc. Pre: pc + 4 <= cp . /** Place four  bytes into code at address pc.
     *  Pre: {@literal pc + 4 <= cp }.
     */
    public void put4(int pc, int od) {
        // pre: pc + 4 <= cp
        put1(pc  , od >> 24);
        put1(pc+1, od >> 16);
        put1(pc+2, od >> 8);
        put1(pc+3, od);
    }

    
Return code byte at position pc as an unsigned int.
/** Return code byte at position pc as an unsigned int.
     */
    private int get1(int pc) {
        return code[pc] & 0xFF;
    }

    
Return two code bytes at position pc as an unsigned int.
/** Return two code bytes at position pc as an unsigned int.
     */
    private int get2(int pc) {
        return (get1(pc) << 8) | get1(pc+1);
    }

    
Return four code bytes at position pc as an int.
/** Return four code bytes at position pc as an int.
     */
    public int get4(int pc) {
        // pre: pc + 4 <= cp
        return
            (get1(pc) << 24) |
            (get1(pc+1) << 16) |
            (get1(pc+2) << 8) |
            (get1(pc+3));
    }

    
Is code generation currently enabled?
/** Is code generation currently enabled?
     */
    public boolean isAlive() {
        return alive || pendingJumps != null;
    }

    
Switch code generation on/off.
/** Switch code generation on/off.
     */
    public void markDead() {
        alive = false;
    }

    
Declare an entry point; return current code pointer
/** Declare an entry point; return current code pointer
     */
    public int entryPoint() {
        int pc = curCP();
        alive = true;
        pendingStackMap = needStackMap;
        return pc;
    }

    
Declare an entry point with initial state;
 return current code pointer
/** Declare an entry point with initial state;
     *  return current code pointer
     */
    public int entryPoint(State state) {
        int pc = curCP();
        alive = true;
        State newState = state.dup();
        setDefined(newState.defined);
        this.state = newState;
        Assert.check(state.stacksize <= max_stack);
        if (debugCode) System.err.println("entry point " + state);
        pendingStackMap = needStackMap;
        return pc;
    }

    
Declare an entry point with initial state plus a pushed value;
 return current code pointer
/** Declare an entry point with initial state plus a pushed value;
     *  return current code pointer
     */
    public int entryPoint(State state, Type pushed) {
        int pc = curCP();
        alive = true;
        State newState = state.dup();
        setDefined(newState.defined);
        this.state = newState;
        Assert.check(state.stacksize <= max_stack);
        this.state.push(pushed);
        if (debugCode) System.err.println("entry point " + state);
        pendingStackMap = needStackMap;
        return pc;
    }


/**************************************************************************
 * Stack map generation
 *************************************************************************/

    
An entry in the stack map. /** An entry in the stack map. */
    static class StackMapFrame {
        int pc;
        Type[] locals;
        Type[] stack;
    }

    
A buffer of cldc stack map entries. /** A buffer of cldc stack map entries. */
    StackMapFrame[] stackMapBuffer = null;

    
A buffer of compressed StackMapTable entries. /** A buffer of compressed StackMapTable entries. */
    StackMapTableFrame[] stackMapTableBuffer = null;
    int stackMapBufferSize = 0;

    
The last PC at which we generated a stack map. /** The last PC at which we generated a stack map. */
    int lastStackMapPC = -1;

    
The last stack map frame in StackMapTable. /** The last stack map frame in StackMapTable. */
    StackMapFrame lastFrame = null;

    
The stack map frame before the last one. /** The stack map frame before the last one. */
    StackMapFrame frameBeforeLast = null;

    
Emit a stack map entry.  /** Emit a stack map entry.  */
    public void emitStackMap() {
        int pc = curCP();
        if (!needStackMap) return;



        switch (stackMap) {
            case CLDC:
                emitCLDCStackMap(pc, getLocalsSize());
                break;
            case JSR202:
                emitStackMapFrame(pc, getLocalsSize());
                break;
            default:
                throw new AssertionError("Should have chosen a stackmap format");
        }
        // DEBUG code follows
        if (debugCode) state.dump(pc);
    }

    private int getLocalsSize() {
        int nextLocal = 0;
        for (int i=max_locals-1; i>=0; i--) {
            if (state.defined.isMember(i) && lvar[i] != null) {
                nextLocal = i + width(lvar[i].sym.erasure(types));
                break;
            }
        }
        return nextLocal;
    }

    
Emit a CLDC stack map frame. /** Emit a CLDC stack map frame. */
    void emitCLDCStackMap(int pc, int localsSize) {
        if (lastStackMapPC == pc) {
            // drop existing stackmap at this offset
            stackMapBuffer[--stackMapBufferSize] = null;
        }
        lastStackMapPC = pc;

        if (stackMapBuffer == null) {
            stackMapBuffer = new StackMapFrame[20];
        } else {
            stackMapBuffer = ArrayUtils.ensureCapacity(stackMapBuffer, stackMapBufferSize);
        }
        StackMapFrame frame =
            stackMapBuffer[stackMapBufferSize++] = new StackMapFrame();
        frame.pc = pc;

        frame.locals = new Type[localsSize];
        for (int i=0; i<localsSize; i++) {
            if (state.defined.isMember(i) && lvar[i] != null) {
                Type vtype = lvar[i].sym.type;
                if (!(vtype instanceof UninitializedType))
                    vtype = types.erasure(vtype);
                frame.locals[i] = vtype;
            }
        }
        frame.stack = new Type[state.stacksize];
        for (int i=0; i<state.stacksize; i++)
            frame.stack[i] = state.stack[i];
    }

    void emitStackMapFrame(int pc, int localsSize) {
        if (lastFrame == null) {
            // first frame
            lastFrame = getInitialFrame();
        } else if (lastFrame.pc == pc) {
            // drop existing stackmap at this offset
            stackMapTableBuffer[--stackMapBufferSize] = null;
            lastFrame = frameBeforeLast;
            frameBeforeLast = null;
        }

        StackMapFrame frame = new StackMapFrame();
        frame.pc = pc;

        int localCount = 0;
        Type[] locals = new Type[localsSize];
        for (int i=0; i<localsSize; i++, localCount++) {
            if (state.defined.isMember(i) && lvar[i] != null) {
                Type vtype = lvar[i].sym.type;
                if (!(vtype instanceof UninitializedType))
                    vtype = types.erasure(vtype);
                locals[i] = vtype;
                if (width(vtype) > 1) i++;
            }
        }
        frame.locals = new Type[localCount];
        for (int i=0, j=0; i<localsSize; i++, j++) {
            Assert.check(j < localCount);
            frame.locals[j] = locals[i];
            if (width(locals[i]) > 1) i++;
        }

        int stackCount = 0;
        for (int i=0; i<state.stacksize; i++) {
            if (state.stack[i] != null) {
                stackCount++;
            }
        }
        frame.stack = new Type[stackCount];
        stackCount = 0;
        for (int i=0; i<state.stacksize; i++) {
            if (state.stack[i] != null) {
                frame.stack[stackCount++] = types.erasure(state.stack[i]);
            }
        }

        if (stackMapTableBuffer == null) {
            stackMapTableBuffer = new StackMapTableFrame[20];
        } else {
            stackMapTableBuffer = ArrayUtils.ensureCapacity(
                                    stackMapTableBuffer,
                                    stackMapBufferSize);
        }
        stackMapTableBuffer[stackMapBufferSize++] =
                StackMapTableFrame.getInstance(frame, lastFrame.pc, lastFrame.locals, types);

        frameBeforeLast = lastFrame;
        lastFrame = frame;
    }

    StackMapFrame getInitialFrame() {
        StackMapFrame frame = new StackMapFrame();
        List<Type> arg_types = ((MethodType)meth.externalType(types)).argtypes;
        int len = arg_types.length();
        int count = 0;
        if (!meth.isStatic()) {
            Type thisType = meth.owner.type;
            frame.locals = new Type[len+1];
            if (meth.isConstructor() && thisType != syms.objectType) {
                frame.locals[count++] = UninitializedType.uninitializedThis(thisType);
            } else {
                frame.locals[count++] = types.erasure(thisType);
            }
        } else {
            frame.locals = new Type[len];
        }
        for (Type arg_type : arg_types) {
            frame.locals[count++] = types.erasure(arg_type);
        }
        frame.pc = -1;
        frame.stack = null;
        return frame;
    }


/**************************************************************************
 * Operations having to do with jumps
 *************************************************************************/

    
A chain represents a list of unresolved jumps. Jump locations
 are sorted in decreasing order.
/** A chain represents a list of unresolved jumps. Jump locations
     *  are sorted in decreasing order.
     */
    public static class Chain {

        
The position of the jump instruction.
/** The position of the jump instruction.
         */
        public final int pc;

        
The machine state after the jump instruction.
 Invariant: all elements of a chain list have the same stacksize
 and compatible stack and register contents.
/** The machine state after the jump instruction.
         *  Invariant: all elements of a chain list have the same stacksize
         *  and compatible stack and register contents.
         */
        Code.State state;

        
The next jump in the list.
/** The next jump in the list.
         */
        public final Chain next;

        
Construct a chain from its jump position, stacksize, previous
 chain, and machine state.
/** Construct a chain from its jump position, stacksize, previous
         *  chain, and machine state.
         */
        public Chain(int pc, Chain next, Code.State state) {
            this.pc = pc;
            this.next = next;
            this.state = state;
        }
    }

    
Negate a branch opcode.
/** Negate a branch opcode.
     */
    public static int negate(int opcode) {
        if (opcode == if_acmp_null) return if_acmp_nonnull;
        else if (opcode == if_acmp_nonnull) return if_acmp_null;
        else return ((opcode + 1) ^ 1) - 1;
    }

    
Emit a jump instruction.
 Return code pointer of instruction to be patched.
/** Emit a jump instruction.
     *  Return code pointer of instruction to be patched.
     */
    public int emitJump(int opcode) {
        if (fatcode) {
            if (opcode == goto_ || opcode == jsr) {
                emitop4(opcode + goto_w - goto_, 0);
            } else {
                emitop2(negate(opcode), 8);
                emitop4(goto_w, 0);
                alive = true;
                pendingStackMap = needStackMap;
            }
            return cp - 5;
        } else {
            emitop2(opcode, 0);
            return cp - 3;
        }
    }

    
Emit a branch with given opcode; return its chain.
 branch differs from jump in that jsr is treated as no-op.
/** Emit a branch with given opcode; return its chain.
     *  branch differs from jump in that jsr is treated as no-op.
     */
    public Chain branch(int opcode) {
        Chain result = null;
        if (opcode == goto_) {
            result = pendingJumps;
            pendingJumps = null;
        }
        if (opcode != dontgoto && isAlive()) {
            result = new Chain(emitJump(opcode),
                               result,
                               state.dup());
            fixedPc = fatcode;
            if (opcode == goto_) alive = false;
        }
        return result;
    }

    
Resolve chain to point to given target.
/** Resolve chain to point to given target.
     */
    public void resolve(Chain chain, int target) {
        boolean changed = false;
        State newState = state;
        for (; chain != null; chain = chain.next) {
            Assert.check(state != chain.state
                    && (target > chain.pc || state.stacksize == 0));
            if (target >= cp) {
                target = cp;
            } else if (get1(target) == goto_) {
                if (fatcode) target = target + get4(target + 1);
                else target = target + get2(target + 1);
            }
            if (get1(chain.pc) == goto_ &&
                chain.pc + 3 == target && target == cp && !fixedPc) {
                // If goto the next instruction, the jump is not needed:
                // compact the code.
                if (varDebugInfo) {
                    adjustAliveRanges(cp, -3);
                }
                cp = cp - 3;
                target = target - 3;
                if (chain.next == null) {
                    // This is the only jump to the target. Exit the loop
                    // without setting new state. The code is reachable
                    // from the instruction before goto_.
                    alive = true;
                    break;
                }
            } else {
                if (fatcode)
                    put4(chain.pc + 1, target - chain.pc);
                else if (target - chain.pc < Short.MIN_VALUE ||
                         target - chain.pc > Short.MAX_VALUE)
                    fatcode = true;
                else
                    put2(chain.pc + 1, target - chain.pc);
                Assert.check(!alive ||
                    chain.state.stacksize == newState.stacksize &&
                    chain.state.nlocks == newState.nlocks);
            }
            fixedPc = true;
            if (cp == target) {
                changed = true;
                if (debugCode)
                    System.err.println("resolving chain state=" + chain.state);
                if (alive) {
                    newState = chain.state.join(newState);
                } else {
                    newState = chain.state;
                    alive = true;
                }
            }
        }
        Assert.check(!changed || state != newState);
        if (state != newState) {
            setDefined(newState.defined);
            state = newState;
            pendingStackMap = needStackMap;
        }
    }

    
Resolve chain to point to current code pointer.
/** Resolve chain to point to current code pointer.
     */
    public void resolve(Chain chain) {
        Assert.check(
            !alive ||
            chain==null ||
            state.stacksize == chain.state.stacksize &&
            state.nlocks == chain.state.nlocks);
        pendingJumps = mergeChains(chain, pendingJumps);
    }

    
Resolve any pending jumps.
/** Resolve any pending jumps.
     */
    public void resolvePending() {
        Chain x = pendingJumps;
        pendingJumps = null;
        resolve(x, cp);
    }

    
Merge the jumps in of two chains into one.
/** Merge the jumps in of two chains into one.
     */
    public static Chain mergeChains(Chain chain1, Chain chain2) {
        // recursive merge sort
        if (chain2 == null) return chain1;
        if (chain1 == null) return chain2;
        Assert.check(
            chain1.state.stacksize == chain2.state.stacksize &&
            chain1.state.nlocks == chain2.state.nlocks);
        if (chain1.pc < chain2.pc)
            return new Chain(
                chain2.pc,
                mergeChains(chain1, chain2.next),
                chain2.state);
        return new Chain(
                chain1.pc,
                mergeChains(chain1.next, chain2),
                chain1.state);
    }


/* **************************************************************************
 * Catch clauses
 ****************************************************************************/

    
Add a catch clause to code.
/** Add a catch clause to code.
     */
    public void addCatch(char startPc, char endPc,
                         char handlerPc, char catchType) {
            catchInfo.append(new char[]{startPc, endPc, handlerPc, catchType});
        }


    public void compressCatchTable() {
        ListBuffer<char[]> compressedCatchInfo = new ListBuffer<>();
        List<Integer> handlerPcs = List.nil();
        for (char[] catchEntry : catchInfo) {
            handlerPcs = handlerPcs.prepend((int)catchEntry[2]);
        }
        for (char[] catchEntry : catchInfo) {
            int startpc = catchEntry[0];
            int endpc = catchEntry[1];
            if (startpc == endpc ||
                    (startpc == (endpc - 1) &&
                    handlerPcs.contains(startpc))) {
                continue;
            } else {
                compressedCatchInfo.append(catchEntry);
            }
        }
        catchInfo = compressedCatchInfo;
    }


/* **************************************************************************
 * Line numbers
 ****************************************************************************/

    
Add a line number entry.
/** Add a line number entry.
     */
    public void addLineNumber(char startPc, char lineNumber) {
        if (lineDebugInfo) {
            if (lineInfo.nonEmpty() && lineInfo.head[0] == startPc)
                lineInfo = lineInfo.tail;
            if (lineInfo.isEmpty() || lineInfo.head[1] != lineNumber)
                lineInfo = lineInfo.prepend(new char[]{startPc, lineNumber});
        }
    }

    
Mark beginning of statement.
/** Mark beginning of statement.
     */
    public void statBegin(int pos) {
        if (pos != Position.NOPOS) {
            pendingStatPos = pos;
        }
    }

    
Force stat begin eagerly
/** Force stat begin eagerly
     */
    public void markStatBegin() {
        if (alive && lineDebugInfo) {
            int line = lineMap.getLineNumber(pendingStatPos);
            char cp1 = (char)cp;
            char line1 = (char)line;
            if (cp1 == cp && line1 == line)
                addLineNumber(cp1, line1);
        }
        pendingStatPos = Position.NOPOS;
    }


/* **************************************************************************
 * Simulated VM machine state
 ****************************************************************************/

    class State implements Cloneable {
        
The set of registers containing values. /** The set of registers containing values. */
        Bits defined;

        
The (types of the) contents of the machine stack. /** The (types of the) contents of the machine stack. */
        Type[] stack;

        
The first stack position currently unused. /** The first stack position currently unused. */
        int stacksize;

        
The numbers of registers containing locked monitors. /** The numbers of registers containing locked monitors. */
        int[] locks;
        int nlocks;

        State() {
            defined = new Bits();
            stack = new Type[16];
        }

        State dup() {
            try {
                State state = (State)super.clone();
                state.defined = new Bits(defined);
                state.stack = stack.clone();
                if (locks != null) state.locks = locks.clone();
                if (debugCode) {
                    System.err.println("duping state " + this);
                    dump();
                }
                return state;
            } catch (CloneNotSupportedException ex) {
                throw new AssertionError(ex);
            }
        }

        void lock(int register) {
            if (locks == null) {
                locks = new int[20];
            } else {
                locks = ArrayUtils.ensureCapacity(locks, nlocks);
            }
            locks[nlocks] = register;
            nlocks++;
        }

        void unlock(int register) {
            nlocks--;
            Assert.check(locks[nlocks] == register);
            locks[nlocks] = -1;
        }

        void push(Type t) {
            if (debugCode) System.err.println("   pushing " + t);
            switch (t.getTag()) {
            case VOID:
                return;
            case BYTE:
            case CHAR:
            case SHORT:
            case BOOLEAN:
                t = syms.intType;
                break;
            default:
                break;
            }
            stack = ArrayUtils.ensureCapacity(stack, stacksize+2);
            stack[stacksize++] = t;
            switch (width(t)) {
            case 1:
                break;
            case 2:
                stack[stacksize++] = null;
                break;
            default:
                throw new AssertionError(t);
            }
            if (stacksize > max_stack)
                max_stack = stacksize;
        }

        Type pop1() {
            if (debugCode) System.err.println("   popping " + 1);
            stacksize--;
            Type result = stack[stacksize];
            stack[stacksize] = null;
            Assert.check(result != null && width(result) == 1);
            return result;
        }

        Type peek() {
            return stack[stacksize-1];
        }

        Type pop2() {
            if (debugCode) System.err.println("   popping " + 2);
            stacksize -= 2;
            Type result = stack[stacksize];
            stack[stacksize] = null;
            Assert.check(stack[stacksize+1] == null
                    && result != null && width(result) == 2);
            return result;
        }

        void pop(int n) {
            if (debugCode) System.err.println("   popping " + n);
            while (n > 0) {
                stack[--stacksize] = null;
                n--;
            }
        }

        void pop(Type t) {
            pop(width(t));
        }

        
Force the top of the stack to be treated as this supertype
 of its current type. /** Force the top of the stack to be treated as this supertype
         *  of its current type. */
        void forceStackTop(Type t) {
            if (!alive) return;
            switch (t.getTag()) {
            case CLASS:
            case ARRAY:
                int width = width(t);
                Type old = stack[stacksize-width];
                Assert.check(types.isSubtype(types.erasure(old),
                                       types.erasure(t)));
                stack[stacksize-width] = t;
                break;
            default:
            }
        }

        void markInitialized(UninitializedType old) {
            Type newtype = old.initializedType();
            for (int i=0; i<stacksize; i++) {
                if (stack[i] == old) stack[i] = newtype;
            }
            for (int i=0; i<lvar.length; i++) {
                LocalVar lv = lvar[i];
                if (lv != null && lv.sym.type == old) {
                    VarSymbol sym = lv.sym;
                    sym = sym.clone(sym.owner);
                    sym.type = newtype;
                    LocalVar newlv = lvar[i] = new LocalVar(sym);
                    newlv.aliveRanges = lv.aliveRanges;
                }
            }
        }

        State join(State other) {
            defined.andSet(other.defined);
            Assert.check(stacksize == other.stacksize
                    && nlocks == other.nlocks);
            for (int i=0; i<stacksize; ) {
                Type t = stack[i];
                Type tother = other.stack[i];
                Type result =
                    t==tother ? t :
                    types.isSubtype(t, tother) ? tother :
                    types.isSubtype(tother, t) ? t :
                    error();
                int w = width(result);
                stack[i] = result;
                if (w == 2) Assert.checkNull(stack[i+1]);
                i += w;
            }
            return this;
        }

        Type error() {
            throw new AssertionError("inconsistent stack types at join point");
        }

        void dump() {
            dump(-1);
        }

        void dump(int pc) {
            System.err.print("stackMap for " + meth.owner + "." + meth);
            if (pc == -1)
                System.out.println();
            else
                System.out.println(" at " + pc);
            System.err.println(" stack (from bottom):");
            for (int i=0; i<stacksize; i++)
                System.err.println("  " + i + ": " + stack[i]);

            int lastLocal = 0;
            for (int i=max_locals-1; i>=0; i--) {
                if (defined.isMember(i)) {
                    lastLocal = i;
                    break;
                }
            }
            if (lastLocal >= 0)
                System.err.println(" locals:");
            for (int i=0; i<=lastLocal; i++) {
                System.err.print("  " + i + ": ");
                if (defined.isMember(i)) {
                    LocalVar var = lvar[i];
                    if (var == null) {
                        System.err.println("(none)");
                    } else if (var.sym == null)
                        System.err.println("UNKNOWN!");
                    else
                        System.err.println("" + var.sym + " of type " +
                                           var.sym.erasure(types));
                } else {
                    System.err.println("undefined");
                }
            }
            if (nlocks != 0) {
                System.err.print(" locks:");
                for (int i=0; i<nlocks; i++) {
                    System.err.print(" " + locks[i]);
                }
                System.err.println();
            }
        }
    }

    static final Type jsrReturnValue = new JCPrimitiveType(INT, null);


/* **************************************************************************
 * Local variables
 ****************************************************************************/

    
A live range of a local variable. /** A live range of a local variable. */
    static class LocalVar {
        final VarSymbol sym;
        final char reg;

        class Range {
            char start_pc = Character.MAX_VALUE;
            char length = Character.MAX_VALUE;

            Range() {}

            Range(char start) {
                this.start_pc = start;
            }

            Range(char start, char length) {
                this.start_pc = start;
                this.length = length;
            }

            boolean closed() {
                return start_pc != Character.MAX_VALUE && length != Character.MAX_VALUE;
            }

            @Override
            public String toString() {
                int currentStartPC = start_pc;
                int currentLength = length;
                return "startpc = " + currentStartPC + " length " + currentLength;
            }
        }

        java.util.List<Range> aliveRanges = new java.util.ArrayList<>();

        LocalVar(VarSymbol v) {
            this.sym = v;
            this.reg = (char)v.adr;
        }
        public LocalVar dup() {
            return new LocalVar(sym);
        }

        Range firstRange() {
            return aliveRanges.isEmpty() ? null : aliveRanges.get(0);
        }

        Range lastRange() {
            return aliveRanges.isEmpty() ? null : aliveRanges.get(aliveRanges.size() - 1);
        }

        void removeLastRange() {
            Range lastRange = lastRange();
            if (lastRange != null) {
                aliveRanges.remove(lastRange);
            }
        }

        @Override
        public String toString() {
            if (aliveRanges == null) {
                return "empty local var";
            }
            StringBuilder sb = new StringBuilder().append(sym)
                    .append(" in register ").append((int)reg).append(" \n");
            for (Range r : aliveRanges) {
                sb.append(" starts at pc=").append(Integer.toString(((int)r.start_pc)))
                    .append(" length=").append(Integer.toString(((int)r.length)))
                    .append("\n");
            }
            return sb.toString();
        }

        public void openRange(char start) {
            if (!hasOpenRange()) {
                aliveRanges.add(new Range(start));
            }
        }

        public void closeRange(char length) {
            if (isLastRangeInitialized() && length > 0) {
                Range range = lastRange();
                if (range != null) {
                    if (range.length == Character.MAX_VALUE) {
                        range.length = length;
                    }
                }
            } else {
                removeLastRange();
            }
        }

        public boolean hasOpenRange() {
            if (aliveRanges.isEmpty()) {
                return false;
            }
            return lastRange().length == Character.MAX_VALUE;
        }

        public boolean isLastRangeInitialized() {
            if (aliveRanges.isEmpty()) {
                return false;
            }
            return lastRange().start_pc != Character.MAX_VALUE;
        }

        public Range getWidestRange() {
            if (aliveRanges.isEmpty()) {
                return new Range();
            } else {
                Range firstRange = firstRange();
                Range lastRange = lastRange();
                char length = (char)(lastRange.length + (lastRange.start_pc - firstRange.start_pc));
                return new Range(firstRange.start_pc, length);
            }
         }

    }

    
Local variables, indexed by register. /** Local variables, indexed by register. */
    LocalVar[] lvar;

    
Add a new local variable. /** Add a new local variable. */
    private void addLocalVar(VarSymbol v) {
        int adr = v.adr;
        lvar = ArrayUtils.ensureCapacity(lvar, adr+1);
        Assert.checkNull(lvar[adr]);
        if (pendingJumps != null) {
            resolvePending();
        }
        lvar[adr] = new LocalVar(v);
        state.defined.excl(adr);
    }

    void adjustAliveRanges(int oldCP, int delta) {
        for (LocalVar localVar: lvar) {
            if (localVar != null) {
                for (LocalVar.Range range: localVar.aliveRanges) {
                    if (range.closed() && range.start_pc + range.length >= oldCP) {
                        range.length += delta;
                    }
                }
            }
        }
    }

    
Calculates the size of the LocalVariableTable.
/**
     * Calculates the size of the LocalVariableTable.
     */
    public int getLVTSize() {
        int result = varBufferSize;
        for (int i = 0; i < varBufferSize; i++) {
            LocalVar var = varBuffer[i];
            result += var.aliveRanges.size() - 1;
        }
        return result;
    }

    
Set the current variable defined state. /** Set the current variable defined state. */
    public void setDefined(Bits newDefined) {
        if (alive && newDefined != state.defined) {
            Bits diff = new Bits(state.defined).xorSet(newDefined);
            for (int adr = diff.nextBit(0);
                 adr >= 0;
                 adr = diff.nextBit(adr+1)) {
                if (adr >= nextreg)
                    state.defined.excl(adr);
                else if (state.defined.isMember(adr))
                    setUndefined(adr);
                else
                    setDefined(adr);
            }
        }
    }

    
Mark a register as being (possibly) defined. /** Mark a register as being (possibly) defined. */
    public void setDefined(int adr) {
        LocalVar v = lvar[adr];
        if (v == null) {
            state.defined.excl(adr);
        } else {
            state.defined.incl(adr);
            if (cp < Character.MAX_VALUE) {
                v.openRange((char)cp);
            }
        }
    }

    
Mark a register as being undefined. /** Mark a register as being undefined. */
    public void setUndefined(int adr) {
        state.defined.excl(adr);
        if (adr < lvar.length &&
            lvar[adr] != null &&
            lvar[adr].isLastRangeInitialized()) {
            LocalVar v = lvar[adr];
            char length = (char)(curCP() - v.lastRange().start_pc);
            if (length < Character.MAX_VALUE) {
                lvar[adr] = v.dup();
                v.closeRange(length);
                putVar(v);
            } else {
                v.removeLastRange();
            }
        }
    }

    
End the scope of a variable. /** End the scope of a variable. */
    private void endScope(int adr) {
        LocalVar v = lvar[adr];
        if (v != null) {
            if (v.isLastRangeInitialized()) {
                char length = (char)(curCP() - v.lastRange().start_pc);
                if (length < Character.MAX_VALUE) {
                    v.closeRange(length);
                    putVar(v);
                    fillLocalVarPosition(v);
                }
            }
            /** the call to curCP() can implicitly adjust the current cp, if so
             * the alive range of local variables may be modified. Thus we need
             * all of them. For this reason assigning null to the given address
             * should be the last action to do.
             */
            lvar[adr] = null;
        }
        state.defined.excl(adr);
    }

    private void fillLocalVarPosition(LocalVar lv) {
        if (lv == null || lv.sym == null || !lv.sym.hasTypeAnnotations())
            return;
        for (Attribute.TypeCompound ta : lv.sym.getRawTypeAttributes()) {
            TypeAnnotationPosition p = ta.position;
            LocalVar.Range widestRange = lv.getWidestRange();
            p.lvarOffset = new int[] { (int)widestRange.start_pc };
            p.lvarLength = new int[] { (int)widestRange.length };
            p.lvarIndex = new int[] { (int)lv.reg };
            p.isValidOffset = true;
        }
    }

    // Method to be called after compressCatchTable to
    // fill in the exception table index for type
    // annotations on exception parameters.
    public void fillExceptionParameterPositions() {
        for (int i = 0; i < varBufferSize; ++i) {
            LocalVar lv = varBuffer[i];
            if (lv == null || lv.sym == null
                    || !lv.sym.hasTypeAnnotations()
                    || !lv.sym.isExceptionParameter())
                continue;

            for (Attribute.TypeCompound ta : lv.sym.getRawTypeAttributes()) {
                TypeAnnotationPosition p = ta.position;
                if (p.hasCatchType()) {
                    final int idx = findExceptionIndex(p);
                    if (idx == -1)
                        Assert.error("Could not find exception index for type annotation " +
                                     ta + " on exception parameter");
                    p.setExceptionIndex(idx);
                }
            }
        }
    }

    private int findExceptionIndex(TypeAnnotationPosition p) {
        final int catchType = p.getCatchType();
        final int startPos = p.getStartPos();
        final int len = catchInfo.length();
        List<char[]> iter = catchInfo.toList();
        for (int i = 0; i < len; ++i) {
            char[] catchEntry = iter.head;
            iter = iter.tail;
            int ct = catchEntry[3];
            int sp = catchEntry[0];
            if (catchType == ct && sp == startPos) {
                return i;
            }
        }
        return -1;
    }

    
Put a live variable range into the buffer to be output to the
 class file.
/** Put a live variable range into the buffer to be output to the
     *  class file.
     */
    void putVar(LocalVar var) {
        // Keep local variables if
        // 1) we need them for debug information
        // 2) it is an exception type and it contains type annotations
        boolean keepLocalVariables = varDebugInfo ||
            (var.sym.isExceptionParameter() && var.sym.hasTypeAnnotations());
        if (!keepLocalVariables) return;
        //don't keep synthetic vars, unless they are lambda method parameters
        boolean ignoredSyntheticVar = (var.sym.flags() & Flags.SYNTHETIC) != 0 &&
                ((var.sym.owner.flags() & Flags.LAMBDA_METHOD) == 0 ||
                 (var.sym.flags() & Flags.PARAMETER) == 0);
        if (ignoredSyntheticVar) return;
        if (varBuffer == null)
            varBuffer = new LocalVar[20];
        else
            varBuffer = ArrayUtils.ensureCapacity(varBuffer, varBufferSize);
        varBuffer[varBufferSize++] = var;
    }

    
Previously live local variables, to be put into the variable table. /** Previously live local variables, to be put into the variable table. */
    LocalVar[] varBuffer;
    int varBufferSize;

    
Create a new local variable address and return it.
/** Create a new local variable address and return it.
     */
    private int newLocal(int typecode) {
        int reg = nextreg;
        int w = width(typecode);
        nextreg = reg + w;
        if (nextreg > max_locals) max_locals = nextreg;
        return reg;
    }

    private int newLocal(Type type) {
        return newLocal(typecode(type));
    }

    public int newLocal(VarSymbol v) {
        int reg = v.adr = newLocal(v.erasure(types));
        addLocalVar(v);
        return reg;
    }

    
Start a set of fresh registers.
/** Start a set of fresh registers.
     */
    public void newRegSegment() {
        nextreg = max_locals;
    }

    
End scopes of all variables with registers ≥ first.
/** End scopes of all variables with registers &ge; first.
     */
    public void endScopes(int first) {
        int prevNextReg = nextreg;
        nextreg = first;
        for (int i = nextreg; i < prevNextReg; i++) endScope(i);
    }

static tables
/**************************************************************************
 * static tables
 *************************************************************************/

    public static String mnem(int opcode) {
        return Mneumonics.mnem[opcode];
    }

    private static class Mneumonics {
        private final static String[] mnem = new String[ByteCodeCount];
        static {
            mnem[nop] = "nop";
            mnem[aconst_null] = "aconst_null";
            mnem[iconst_m1] = "iconst_m1";
            mnem[iconst_0] = "iconst_0";
            mnem[iconst_1] = "iconst_1";
            mnem[iconst_2] = "iconst_2";
            mnem[iconst_3] = "iconst_3";
            mnem[iconst_4] = "iconst_4";
            mnem[iconst_5] = "iconst_5";
            mnem[lconst_0] = "lconst_0";
            mnem[lconst_1] = "lconst_1";
            mnem[fconst_0] = "fconst_0";
            mnem[fconst_1] = "fconst_1";
            mnem[fconst_2] = "fconst_2";
            mnem[dconst_0] = "dconst_0";
            mnem[dconst_1] = "dconst_1";
            mnem[bipush] = "bipush";
            mnem[sipush] = "sipush";
            mnem[ldc1] = "ldc1";
            mnem[ldc2] = "ldc2";
            mnem[ldc2w] = "ldc2w";
            mnem[iload] = "iload";
            mnem[lload] = "lload";
            mnem[fload] = "fload";
            mnem[dload] = "dload";
            mnem[aload] = "aload";
            mnem[iload_0] = "iload_0";
            mnem[lload_0] = "lload_0";
            mnem[fload_0] = "fload_0";
            mnem[dload_0] = "dload_0";
            mnem[aload_0] = "aload_0";
            mnem[iload_1] = "iload_1";
            mnem[lload_1] = "lload_1";
            mnem[fload_1] = "fload_1";
            mnem[dload_1] = "dload_1";
            mnem[aload_1] = "aload_1";
            mnem[iload_2] = "iload_2";
            mnem[lload_2] = "lload_2";
            mnem[fload_2] = "fload_2";
            mnem[dload_2] = "dload_2";
            mnem[aload_2] = "aload_2";
            mnem[iload_3] = "iload_3";
            mnem[lload_3] = "lload_3";
            mnem[fload_3] = "fload_3";
            mnem[dload_3] = "dload_3";
            mnem[aload_3] = "aload_3";
            mnem[iaload] = "iaload";
            mnem[laload] = "laload";
            mnem[faload] = "faload";
            mnem[daload] = "daload";
            mnem[aaload] = "aaload";
            mnem[baload] = "baload";
            mnem[caload] = "caload";
            mnem[saload] = "saload";
            mnem[istore] = "istore";
            mnem[lstore] = "lstore";
            mnem[fstore] = "fstore";
            mnem[dstore] = "dstore";
            mnem[astore] = "astore";
            mnem[istore_0] = "istore_0";
            mnem[lstore_0] = "lstore_0";
            mnem[fstore_0] = "fstore_0";
            mnem[dstore_0] = "dstore_0";
            mnem[astore_0] = "astore_0";
            mnem[istore_1] = "istore_1";
            mnem[lstore_1] = "lstore_1";
            mnem[fstore_1] = "fstore_1";
            mnem[dstore_1] = "dstore_1";
            mnem[astore_1] = "astore_1";
            mnem[istore_2] = "istore_2";
            mnem[lstore_2] = "lstore_2";
            mnem[fstore_2] = "fstore_2";
            mnem[dstore_2] = "dstore_2";
            mnem[astore_2] = "astore_2";
            mnem[istore_3] = "istore_3";
            mnem[lstore_3] = "lstore_3";
            mnem[fstore_3] = "fstore_3";
            mnem[dstore_3] = "dstore_3";
            mnem[astore_3] = "astore_3";
            mnem[iastore] = "iastore";
            mnem[lastore] = "lastore";
            mnem[fastore] = "fastore";
            mnem[dastore] = "dastore";
            mnem[aastore] = "aastore";
            mnem[bastore] = "bastore";
            mnem[castore] = "castore";
            mnem[sastore] = "sastore";
            mnem[pop] = "pop";
            mnem[pop2] = "pop2";
            mnem[dup] = "dup";
            mnem[dup_x1] = "dup_x1";
            mnem[dup_x2] = "dup_x2";
            mnem[dup2] = "dup2";
            mnem[dup2_x1] = "dup2_x1";
            mnem[dup2_x2] = "dup2_x2";
            mnem[swap] = "swap";
            mnem[iadd] = "iadd";
            mnem[ladd] = "ladd";
            mnem[fadd] = "fadd";
            mnem[dadd] = "dadd";
            mnem[isub] = "isub";
            mnem[lsub] = "lsub";
            mnem[fsub] = "fsub";
            mnem[dsub] = "dsub";
            mnem[imul] = "imul";
            mnem[lmul] = "lmul";
            mnem[fmul] = "fmul";
            mnem[dmul] = "dmul";
            mnem[idiv] = "idiv";
            mnem[ldiv] = "ldiv";
            mnem[fdiv] = "fdiv";
            mnem[ddiv] = "ddiv";
            mnem[imod] = "imod";
            mnem[lmod] = "lmod";
            mnem[fmod] = "fmod";
            mnem[dmod] = "dmod";
            mnem[ineg] = "ineg";
            mnem[lneg] = "lneg";
            mnem[fneg] = "fneg";
            mnem[dneg] = "dneg";
            mnem[ishl] = "ishl";
            mnem[lshl] = "lshl";
            mnem[ishr] = "ishr";
            mnem[lshr] = "lshr";
            mnem[iushr] = "iushr";
            mnem[lushr] = "lushr";
            mnem[iand] = "iand";
            mnem[land] = "land";
            mnem[ior] = "ior";
            mnem[lor] = "lor";
            mnem[ixor] = "ixor";
            mnem[lxor] = "lxor";
            mnem[iinc] = "iinc";
            mnem[i2l] = "i2l";
            mnem[i2f] = "i2f";
            mnem[i2d] = "i2d";
            mnem[l2i] = "l2i";
            mnem[l2f] = "l2f";
            mnem[l2d] = "l2d";
            mnem[f2i] = "f2i";
            mnem[f2l] = "f2l";
            mnem[f2d] = "f2d";
            mnem[d2i] = "d2i";
            mnem[d2l] = "d2l";
            mnem[d2f] = "d2f";
            mnem[int2byte] = "int2byte";
            mnem[int2char] = "int2char";
            mnem[int2short] = "int2short";
            mnem[lcmp] = "lcmp";
            mnem[fcmpl] = "fcmpl";
            mnem[fcmpg] = "fcmpg";
            mnem[dcmpl] = "dcmpl";
            mnem[dcmpg] = "dcmpg";
            mnem[ifeq] = "ifeq";
            mnem[ifne] = "ifne";
            mnem[iflt] = "iflt";
            mnem[ifge] = "ifge";
            mnem[ifgt] = "ifgt";
            mnem[ifle] = "ifle";
            mnem[if_icmpeq] = "if_icmpeq";
            mnem[if_icmpne] = "if_icmpne";
            mnem[if_icmplt] = "if_icmplt";
            mnem[if_icmpge] = "if_icmpge";
            mnem[if_icmpgt] = "if_icmpgt";
            mnem[if_icmple] = "if_icmple";
            mnem[if_acmpeq] = "if_acmpeq";
            mnem[if_acmpne] = "if_acmpne";
            mnem[goto_] = "goto_";
            mnem[jsr] = "jsr";
            mnem[ret] = "ret";
            mnem[tableswitch] = "tableswitch";
            mnem[lookupswitch] = "lookupswitch";
            mnem[ireturn] = "ireturn";
            mnem[lreturn] = "lreturn";
            mnem[freturn] = "freturn";
            mnem[dreturn] = "dreturn";
            mnem[areturn] = "areturn";
            mnem[return_] = "return_";
            mnem[getstatic] = "getstatic";
            mnem[putstatic] = "putstatic";
            mnem[getfield] = "getfield";
            mnem[putfield] = "putfield";
            mnem[invokevirtual] = "invokevirtual";
            mnem[invokespecial] = "invokespecial";
            mnem[invokestatic] = "invokestatic";
            mnem[invokeinterface] = "invokeinterface";
            mnem[invokedynamic] = "invokedynamic";
            mnem[new_] = "new_";
            mnem[newarray] = "newarray";
            mnem[anewarray] = "anewarray";
            mnem[arraylength] = "arraylength";
            mnem[athrow] = "athrow";
            mnem[checkcast] = "checkcast";
            mnem[instanceof_] = "instanceof_";
            mnem[monitorenter] = "monitorenter";
            mnem[monitorexit] = "monitorexit";
            mnem[wide] = "wide";
            mnem[multianewarray] = "multianewarray";
            mnem[if_acmp_null] = "if_acmp_null";
            mnem[if_acmp_nonnull] = "if_acmp_nonnull";
            mnem[goto_w] = "goto_w";
            mnem[jsr_w] = "jsr_w";
            mnem[breakpoint] = "breakpoint";
        }
    }
}